The change in the tropical Hadley cell since 1950 is examined within the
context of the long-term warming in global surface temperatures. The
study involves analyses of observations, including various metrics of the
Hadley cell, and ensemble 50-year simulations by an atmospheric general
circulation model (AGCM) forced with the observed evolution of global
sea surface temperature since 1950. Consistent evidence is found for an
intensification of the Northern Hemisphere winter Hadley cell since 1950.
This is shown to be an atmospheric response to the observed tropical
ocean warming trend, together with an intensification of El Niño's
interannual fluctuations, including larger amplitude and increased
frequency after 1976. The intensification of the winter Hadley cell is
shown to be associated with an intensified hydrological cycle consisting
of increased equatorial oceanic rainfall, and a general drying of
tropical/subtropical landmasses. This Hadley cell change is consistent
with previously documented dynamic changes in the extratropics, including
a strengthening of westerly atmospheric flow and an intensification of
mid-latitude cyclones.